Problem: $ { \left[\begin{array}{rrr}{1} & {-1} & {-2} \\ {2} & {3} & {1}\end{array}\right]+\left[\begin{array}{rrr}{-2} & {-1} & {0} \\ {0} & {0} & {-2}\end{array}\right] = {?} } $
Explanation: To find the sum of two matrices, add the corresponding items between each matrix. ${\left[\begin{array}{rrr}{1}+{-2} & {-1}+{-1} & {-2}+{0} \\ {2}+{0} & {3}+{0} & {1}+{-2}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rrr}{-1} & {-2} & {-2} \\ {2} & {3} & {-1}\end{array}\right]}$